Upgrade our copies of clang, llvm, lldb and compiler-rt to r312293 from
the upstream release_50 branch. This corresponds to 5.0.0 rc4.
As of this version, the cad/stepcode port should now compile in a more
reasonable time on i386 (see bug 221836 for more information).
PR: 221836
MFC after: 2 months
X-MFC-with: r321369